1. Field of the Invention
This invention generally relates to devices that measure fluid properties. Here, the present invention is used to simulate the reservoir conditions of pressure and temperature and to measure fluid properties within a sample.
2. Background Information
The high-pressure, visual cell is a very useful device in the petroleum industry. It is used to simulate the underground reservoir conditions of pressure (P) and temperature (T), to measure fluid properties such as density, viscosity and interfacial tension, etc., as well as in situ visual observation of the test specimen. This information is very important for the optimization of production from such reservoirs.
The existing industrial equipment for measuring fluid properties is generally limited to pressures of 70-80 MPa (10.2-11.6 kpsi) and temperatures of 150.degree. C. (302.degree. F.) and is useful for simulating reservoir conditions with pressures and temperatures less than the specified limits. However, recent discoveries have found reservoirs with pressures up to 18,000 psi (124 MPa) and temperatures up to 370.degree. F. (188.degree. C.). Obviously, for accurate measurements, the existing equipment is not adequate for the higher temperatures and pressures.
Most of these existing visual cells have a typical sample volume of 50 cc (1" diameter and 7" long cell). Frequently, the samples are transferred via a sample retrieving tube to other devices that are held at the same P/T condition and which measure density, viscosity and interfacial tension, etc. Such procedures are usually time consuming, and in many cases, the experimental conditions are not completely identical to each other. Furthermore, the massive equipment that have large samples under compression store a considerable amount of energy which creates a hazardous condition. These hazards require extra safety shields to protect the equipment operators from being injured.
Looking into the future, there is a need to improve the system for measurements of the fluid properties. The continuing evolution will involve: miniaturizing equipment and samples to reduce the problems inherent in constructing massive equipment and preparing large samples, measuring with nondestructive methods to prevent altering the overall composition of the fluids, increasing accuracy and efficiency of the experimental measurements, and reducing the time required and cost involved in all of these operations.
The general idea is to have a small pressure cell that is capable of measuring everything in a short time. The present invention addresses such a challenge by proposing a conceptual design of a miniature high-pressure, visual cell combining all the measuring devices into just one probe; i.e., a laser beam of suitable frequency for measuring all quantities of viscosity, interfacial tension, density, and equation of state of the fluids.
The present proposed design of the miniature visual cell for petroleum reservoir fluid studies is inspired from the diamond anvil press now widely used in the high-pressure research community. A typical diamond press is shown in FIG. 1. It consists of two brilliant cut single crystal diamond anvils with metal gaskets sandwiched in between them. The sample chamber is typically several hundred microns (.mu.m) diameter and 20-100 .mu.m thick. Such a press or press of similar design was first used by Van Valkenburg [A. Van Valkenburg, in "High Pressure Measurement" pp. 87-84, ed. by A. Giardini and E. C. Lloyd, Butterworth, Washington (1963)] and others [C. E. Weir, E. R. Lippincott, A. Van Valkenburg, and E. N. Bunting, A 63 J. Res. Natl. Bur. Stand. Sect. p. 55 (1959), see also Weir et al., U.S. Pat. No. 3,079,505]. Later, Piermarini et al. [G. J. Piermarini, R. A. Forman, and S. Block, Rev. Sci. Instrum. 49, p. 1061 (1978)] showed that the ruby fluorescence shift induced by pressure can be used as a secondary pressure scale up to 300 kbar (4.3.times.10.sup.6 psi), and Mao and Bell [H. K. Mao and P. M. Bell, Science 191, p. 851 (1976), Xu et al., Science 232, p. 1404 (1986), see also Bell et al., U.S. Pat. No. 4,339,252] further extended the pressure capability to over 1 Mbar (14.5.times.10.sup.6 psi). In the last three to four years, the diamond press has become a very popular tool in the high pressure research community for X-ray diffraction, optical (Raman and Brillouin), resistivity and magnetic studies for various physical phenomena such as phase transformation, reaction kinetics, electron and phonon transport properties and superconductivity, etc. For a general discussion on this subject, see A. Jayaraman, The Diamond-Anvil High-Pressure Cell, Sci. Amer. 250, 54 (April 1984).
Of course, such a design will not be suitable for petroleum reservoir fluid studies because the fluid sample needs to be transferred under pressure and the chamber volume of the diamond press is too small. The general approach of the present invention is to use the sapphire anvils instead of the diamond anvils, and to scale up the cell size with a volume of approximately several cubic centimeters. This is suitable for the sample transfer and all the required measurements, but yet it is ten times smaller than the conventional visual cell.